Find Out How a Variable-Speed Furnace Works in Your Home

December 29, 2015
By
Roth Heating & Cooling, Plumbing & Electrical

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A variable-speed furnace offers quiet, energy efficient comfort using advanced
motor technology. Instead of only running on top speed, a furnace equipped
with an electronically-commutated motor (ECM) will adjust its running
speeds based on your home’s need for heat. They save energy because
ECMs use much less electricity than the standard motor, and its slower
running speed helps distribute the heat more evenly.

What a Variable-Speed Furnace Does

Conventional blower motors, known as permanent split capacitor motors (PSCs)
use alternating current (AC) while an ECM uses direct current (DC). Since
our power supply is AC, the variable-speed furnace motor has an inverter
that changes the power flow to DC, which is a
more efficient use of electricity.

These motors also include high tech components that work with the HVAC
system to sense how much heated air your home needs, and adjust their
running speeds accordingly. If it’s just a few degrees, the motor
will run at a slower speed. The ECM is also capable of sensing the airflow
through the blower, making adjustments for constricted airflow from dirt
filters or blocked return registers.

Variable-Speed Advantages

Cleaner air. Since a variable-speed furnace runs more slowly, it removes more airborne
particulates, which creates a healthier home. Anyone who suffers from
allergies to pollen, dander or mold may breathe easier.

Less electrical consumption. Although combustion furnace efficiency isn’t measured by its electrical
use alone, your monthly energy bills will drop. If the furnace is equipped
with an air conditioning system, your summer cooling costs will also decline.
These systems also remove more humidity in the cooling mode since the
air handler runs longer.

Quiet operation. These systems start and stop their cycles slowly. Even at top speeds,
these motors are quieter than PSC motors.

Durability. HVAC systems with variable-speed motors tend to last longer since they
avoid the stress and wear that frequent starts cause.